While the present invention is not limited to any particular type of energy converter, it will be described herein in connection with a undirectional energy converter such as that shown in U.S. Pat. No. 3,859,789, issued Jan. 14, 1975. In an energy converter of this type, a closed, continuous loop passageway contains a plurality of freely-movable bodies which travel around the passageway in one direction only. Force is applied to successive ones of the bodies in one region of the passageway to thereby propel them around the passageway. At points around the passageway, at least a portion of the kinetic energy of the propelled bodies is converted into another form of energy. Thereafter, successive ones of the bodies are returned back to the starting region where they are again propelled in one direction by application of a force thereto. The unidirectional energy converter shown in the aforesaid patent may be operated in accordance with various well-known thermodynamic cycles such as the Brayton, Otto and Diesel cycles. Such thermodynamic cycles employ adiabatic expansion of a gas during the power stroke. This is followed by an exhaust stroke, during which heat is rejected, and adiabatic compression back to a higher pressure. With isothermal compression of a gas, however, variations can be visualized in thermodynamic cycles which more closely approximate the Carnot cycle.